(1) Field of the Invention
This invention relates to a magnetoresistive head, and more particularly to a magnetic head of the kind described above which comprises an elongate magnetoresistive element of a magnetically anisotropic material having terminals at its ends for connection to a current source and means for supplying sense current to this magnetoresistive element for reproducing information recorded on a magnetic recording medium.
(2) Description of the Prior Art
Magnetoresistive heads utilizing the magnetoresistance effect of a thin film of a ferromagnetic material such as permalloy are now attracting attention in the field of high-density information recording by virtue of the excellent performance including the high sensitivity and the independence of the output from the moving speed of a magnetic recording medium. Such a magnetic head is known from the disclosure of, for example, U.S. Pat. No. 4,052,748.
A Barberpole magnetoresistive head, which is an example of such a magnetic head, will be described with reference to FIGS. 1 and 2. Referring to FIG. 1, the magnetoresistive head designated generally by a reference numeral 10 comprises a substrate 70 of a material such as glass, a magnetoresistive element 30 whose electrical resistance varies when a magnetic recording medium 20 moves relative thereto, and a pair of conductive terminals 40 and 50 connected to the both ends respectively of the magnetoresistive element 30. This magnetoresistive element 30 is electrically connected to a detecting circuit 60 via the conductive terminals 40 and 50, and a plurality of short bars 80 are provided on the element 30 in a relation making an angle with the element 30 and spaced apart from each other by a predetermined distance. Each of these short bars 80 is composed of a conductive strip making a preferable angle of 45.degree. with the longitudinal axis of the magnetoresistive element 30. The magnetoresistive element 30 has generally a rectangular shape in front elevation as seen in FIG. 2a and is formed so that its major axis or longitudinal axis coincides with the easy axis of magnetization A.
A sense current supplied from the detecting circuit 60 to the magnetoresistive head 10 having the construction described flows above though the magnetoresistive element 30 in a direction orthogonal with respect to the short bars 80 to produce a magnetic bias field along substantially the longitudinal axis of the magnetoresistive element 30. Under the influence of the thus produced magnetic bias field, the magnetic recording medium 20 is moved or rotated relative to the magnetoresistive head 10, and the resultant variations of the resistance value of the magnetoresistive element 30 are detected by the detecting circuit 60. In this manner, the magnetoresistive head 10 reproduces information recorded on the magnetic recording medium 20.
However, the magnetoresistive element 30 of the prior art magnetoresistive head 10 tends to have a closure magnetic domain structure as shown in FIG. 2b after the application of the magnetic field in the direction of the hard axis of magnetization B, and, as a result, domain walls 2 extending toward the corners of the ends 30a and 30b of the magnetoresistive element 30 tend to be formed. The process of formation of such domain walls will now be explained in order.
(a) The application of the magnetic field in the direction of the hard axis of magnetization B causes inclination of the direction of magnetization having been oriented in the direction of the easy axis of magnetization A.
(b) When the application of the magnetic field is then stopped after the inclination has attained 90.degree., four magnetic domains having different directions of magnetization 21 appear, since the magnetization tends to circulate within the magnetoresistive element 30 before stabilization.
(c) As a result, domain walls 2 as shown in FIG. 2b are formed at the boundaries between the magnetic domains.
Thus, domain walls tend to be formed also in the end portions of the magnetoresistive element 30 of the prior art magnetoresistive head 10. Because of the fact that especially the central domain wall among those formed in the magnetoresistive element acts to cause variation of the level of the output from the magnetic head and also gives rise to generation of the Barkhousen noise, it is strongly demanded to suppress formation of such undesirable domain walls.
As a means for suppressing formation of such undesirable domain walls, a method has been proposed according to which a single-domain structure is obtained by externally applying a magnetic bias field in the direction of the easy axis of magnetization of the magnetoresistive element.
However, the proposed method is not applicable to a magnetic head designed for the reproduction of information recorded in a high recording density on a magnetic recording medium. This is because, in such a magnetic head designed for the reproduction of high-density recorded information, shielding films are formed on both sides of the magnetoresistive element while defining a narrow gap therebetween, and, due to the absorption of the magnetic flux by the shielding films, the magnetoresistive element is not effectively energized.
On the other hand, in a Barberpole magnetoresistive head as disclosed in the above-mentioned U.S. Pat. No. 4,052,748, it is theoretically possible to suppress formation of undesirable domain walls by increasing the value of a sense current supplied to the magnetoresistive element thereby increasing the strength of the magnetic bias field applied in the direction of the easy axis of magnetization. Actually, however, when the current density of the detecting current supplied to the magnetoresistive element exceeds an allowable limit which is, for example, 5.times.10.sup.6 A/cm.sup.2 when the magnetoresistive element is in the form of a thin film of permalloy, the magnetoresistive element is liable to be destroyed by being heated by the excessive Joule heat and also due to the electromigration, and it has thus been impossible to completely suppress formation of undesirable domain walls in the magnetoresistive element of the prior art magnetoresistive head.